I'm not sure if it's a SCLogin issue either. The simplest way to narrow things down is to simply implement the standard Joomla mod_login module with the same parameters. If it has the same issue, then that would narrow it down to a permissions issue, a redirect or SEF issue, or something else along those lines.
Let us know how the mod_login test goes and we'll gladly investigate further if it's specific to our extensions.
Thanks,
Alex